You should explore Meghalaya especially Cherapunji where you can find nature at its best along with several waterfalls. it can also be covered within 5 days.
North east sikkim Lachung and Lachen will be best for you. If you want to explore more of north east, you can have a look to this informative video I found on youtube https://youtu.be/iCNE-aI05PY
Kindly skip the cruise for Sunset .. it' will be better if you climb on the top of the Santorini ..there is a dedicated space where people gather for the sunset view ..
If you are traveling from Bangalore or Eastern Coastal Road, the roads are superb. You might be traveling faster than what your Google navigation will say.
But, if you are travelling from Kochi/Western Coastal Road, it is a single road. Roads are good, but with a heavy traffic through out the day.
What other locations you can visit depends totally on which route you're gonna follow.
Hey Tushar,
In my opinion, Mcleodganj is a clear winner. Situated above Dharamshala, the town has a number of experiences to offer to travellers of all kinds. Whether you're seeking an escape into spirituality, want to undertake an adventure or simply want to relax and indulge in great food, Mcleodganj has it all. It is ideal for solo trips, family vacation and even for a couple getaway. In fact, I spent one month in that beautiful town and had the time of my life.
I wrote an article a while back talking about my favourite hidden gems, do check it out: https://www.tripoto.com/trip/exploring-hidden-treasures-of-mcleodganj-5982d4c6b865
Hope you have a great trip!